1. Field of the Invention
This invention is related in general to the field of counter-rotating engines and, in particular, to a novel configuration for a 2 cycle engine with a novel mounting system, and one or more sets of simultaneously firing cylinders, that enables the advantageous counter-rotation of the engine's shaft and block for suitable applications.
2. Description of the Related Art
All internal combustion engines share the characteristic of transforming the pressure generated by the combustion of a fuel into the useful rotation of a shaft. Piston engines cause the rotation of the shaft by expanding the combustion gases between a stationary cylinder and a movable piston connected to the eccentric of a rotating output shaft.
Thus, in typical applications the engine is firmly mounted on a support structure and delivers power to a useful load by means of a rotating output shaft. In aviation applications, the engine is attached to the body of the aircraft and a propeller is mounted on the shaft to produce propulsion. As a result of the torque produced by the operation of the engine on the rotating shaft and propeller, an opposite reactive torque is produced on the stationary parts of the engine and is transmitted to the frame of the airplane to which it is attached.
Aviation engineers have long searched for ways to reduce the instability that results from this reactive torque. One way has been to provide two propellers that rotate in opposite directions to produce symmetrical counter-balancing actions and reactions, either in twin-engine or in single-engine configurations. The twin-engine solution can obviously be implemented with any kind of power plant, including reciprocating-piston engines, simply by providing opposite directions of propeller rotation in each engine.
See, for example, the solutions provided by Escher (U.S. Pat. No. 1,052,658), Conill (U.S. Pat. No. 1,151,568), Exel (U.S. Pat. No. 1,561,424), Hockney (U.S. Pat. No. 2,336,787), Muffly (U.S. Pat. No. 2,419,787), Olcott (U.S. Pat. No. 2,838,123), Conkle (U.S. Pat. No. 3,554,666), Keever (U.S. Pat. No. 6,193,189), Canton (French Patent No. 397,499), Warren (U.S. Pat. No. 6,209,495-B1), Zornes (U.S. Pat. No. 5,456,076), and Mouton (U.S. Pat. No. 5,535,715). None of these patents describe engines which wherein the internal fluid flows are deliberately directed toward the combustion chamber by centrifical forces my manipulating the internal surfaces defining the engine intake manifolds and crankcase volumes as described in the present invention.
The majority of these patents describe predominantly 4 cycle reciprocating-piston engines designed to balance opposing torque, either by means of two counter-rotating output shafts connected to multiple crankshafts originating from a stationary enclosure, or by a rotating crankshaft cooperating with a counter-rotating combustion-chamber enclosure. All of the various solutions disclosed in these patents involve complicated engine mounting, inlet/exhaust porting and lubricating systems that have greatly affected their practical implementation.
The single-engine, counter-rotating propeller propulsion solution has been explored in aviation technology by allowing both the rotation of the crankshaft and the counter-rotation of the cylinders of a reciprocating-piston engine. This approach involves counter-rotating structures (engine block and crankshaft) which support two propellers rotating in opposite directions to each other, which results in a greater amount of propelling force and a substantially perfect torque balance. To that end, the combustion-chamber/crankcase configuration of internal-combustion engines has been modified in various manners over the years attempting to attain a well balanced counter-rotating propeller system.
Some engines, reciprocating piston or otherwise, are more suitable than others for counter-rotation. Four cycle piston engines are an example of an engine type unsuitable for block counter-rotation. The mechanical configuration of 4 cycle reciprocating-piston engines, which comport the use of pistons traveling radially with respect to the axis of rotation of the crankshaft, and include one or more reservoir of oil for lubrication, produce an inherently unsuitable engine. Each piston operates radially from a corresponding crank in the output shaft, access to the combustion chamber for fuel delivery is necessarily limited to the distal end of each cylinder, which creates access difficulties during rotation of the cylinders and intake flow difficulties since flow to the combustion chamber is necessarily against centrifical force.
Lubrication is similarly complicated by centrifical-force effects that cause crankcase oil, necessary for lubrication, usually pooled in a reservoir below the crankshaft and away from the pistons, to accumulate in various locations, away from the crankshaft, including behind the pistons. Centrifical force acting upon accumulations of oil at this location causes severe engine imbalances, and also directly opposes the desires action created from internal combustion. Accordingly, no counter-rotating engine has been successfully implemented commercially using 4 cycle reciprocating-piston configurations in spite of the theoretical advantages provided by this concept.
Different from 4 cycle piston engines, Two cycle engines are an example of an engine type suitable for block counter-rotation.
Two cycle piston engines do not employ the crankcase volume to contain a constant reservoir of lubricating oil. The lubricating oil is atomized with the fuel-air mixture and transits the crankcase providing lubrication en route to the combustion chamber. Although this eliminates the adverse effects of centrifical forces acting upon a constant reservoir of lubricating oil within the crankcase volume, cavities within the crankcase are still able to trap transit fluids which inhibit oil flow and create fluid build-ups and imbalances during engine operation. Current technology in the crank case design includes cavities and interior surfaces which during rotation are able to pool fluids such as fuel and oil against surfaces away from the center of rotation, most notably the back side of the piston faces. Reservoirs of oil under the influence of centrifical force adversely affects the balance of the crankcase and inhibits the reciprocating motion of the pistons.
It is noted full scale 2-cycle engines operate at substantially higher RPM's than optimum for propeller efficiency. Standard output shaft designs require a reduction gear ranging from 2:1 to almost 4:1. Because 2-cycle engines have a greater weight to power ratio than 4 cycle engines, they remain competitive with weight to power ratios of 4 cycle engines, even with the addition of a crankshaft speed reduction unit.
The only examples of counter-rotating 2 cycle piston engines are by model airplane enthusiast utilizing radically simplified 2 cycle model airplane engines; the Cox 0.049 2 cycle piston engines wherein the block revolutions are slow, the engines are small, and the propellers are small (requiring no rear reduction) and the centrifical forces are minimal. In this example, an unmodified 0.049 engine, equipped with a small propeller in its output shaft, is mounted, by the usual engine block motor mounts, to the center hub of a very large, helicopter type rotating propeller wherein the two propellers are concentric. The helicopter blade is counter pitched such that during normal engine operation the opposing torque produced by the engine is transmitted to the helicopter blade and dissipated into the air as thrust by turning the helicopter blade. In this configuration the helicopter blade and the attached engine block are turning substantially slower and the distance from the center of rotation is small, and the lower centrifical forces generated by the slower RPM allows the engine to essentially function normally. It has been noted the engine functions progressively less normally at higher block RPMs likely due to adverse reaction to increasing centrifical forces acting upon the fuel/oil mixture. These small 2 cycle engines are significantly simpler than typical 2 cycle engines; the entire electrical system is removed and replaced by a glow plugs, and other exterior accessories, such as the starter, alternator, fuel pump etc, are eliminated.
No fully accessorized, full functioning, full scale counter-rotating engine has been successfully implemented commercially using 2 cycle reciprocating-piston configurations in spite of the theoretical application to aviation provided by this concept.
Therefore, there is still an opportunity for a better implementation of the counter-rotating piston engine approach for aviation propulsion. This invention is directed at providing a novel approach based on the redesign of the 2 cycle engine crankcase, and pistons to disallow the adverse accumulation of fluids during engine operation, and in doing so, to advantageously utilize the centrifical forces of the rotating block to aid in the transfer of fluids to the combustion chamber during operation.